Now, it is clear to me that a Christian can be defined in few words like this:
A person who pledged absolute trust in the truth.
A Christian is a person who believe that truth is the very word/language of God. In truth, the Word, God created all things, and in it He hold all things together. The Word is God and the Word incarnated and became man:Jesus.
 In the beginning was the Word, and the Word was with God, and the Word was God.  The same was in the beginning with God.  All things were made by him: and without him was made nothing that was made.  In him was life, and the life was the light of men.  And the light shineth in darkness, and the darkness did not comprehend it.John 1
In Jesus, the truth, the divine language, is translated into human language. We can look at him, his life, from beginning to end, and understand the message of God to us.
Jesus said: "I am the way, and the truth and the life."
This means that for a Christian, true life, eternal life, is in the truth. This imply that true death is in lie(s). For these reasons, saints were never people who were afraid of physical death, they were afraid of spiritual death. They were afraid of lying and finding themselves in lies and falsehoods, embracing them and living by them.
In the same faith, for a saint to love is not to spare people so much from physical death as from spiritual death.
For a saint, it is not an absolute necessity to save physical lives (his or of his beloved people), but it is an absolute necessity to save them from spiritual death:lies and deceptions.
For a saint, walking in the truth is walking in the street that lead to Paradise. One must stay on this street and if necessary die on it. One must not leave it even to spare some physical lives of someone else. This street is Jesus himself. It is in Jesus that life is.
On the other hand, if one exit and walk away from this street by walking in falsehood, they are walking away from eternal life, and therefore they are dying as they walk away. The devil 'kills' us by setting up these falsehood and proposing that we walk in them. Jesus said that the devil is 'a liar and murderer' from the beginning. He lead us into death by the way of lies and deceits.
I find that the best tactic of the devil is to scare us to death.
The Bible tells us that the devil "holds the world in captivity through the fear of death." (Heb 2.15) We always feel a need to lie because we are scared to 'death' about something. It seems that the only alternatives are a lie or a 'death'. This is where we need faith. Faith is about trusting God always, trusting that he hold everything in his hands. Faith is about trust in the truth, because we know that nothing can hold without the truth, we know that the truth is the very Word of God. Faith is trust in the Word of God no matter what. And sometimes we are called to witness that this Word is powerful even in death and beyond death. Dying in truth is being sealed in eternal life. Again, life is not physical integrity, but spiritual integrity. Because with spiritual integrity, physical integrity can always be restored, in other words, the resurrection of the body. But when spiritual integrity is lost through falsehood, there is no hope of future physical integrity. We will rise to witness judgment which will be eternal disintegration, eternal incoherency, "the worm will never die"(Mrk 9.48)It is this sealing of loss of spiritual integrity which also affects physical integrity which is called Hell.
In consideration of all this, absolute trust in truth is necessary for salvation. This is the summary of the Christian Faith. So a Christian believes that there is no salvation without Jesus Christ.
When faced with classical questions like: "how to save Jew from Nazi?" without lying, we must remember to ask ourselves who is the greater enemy of the Jew, the nazi or the devil? Also, some them from what death? physical first or spiritual first? First, with God's grace, I would remind them to trust God, that God is on the other side as well, so nothing to fear than betraying God. Next, I will try my best to honor the truth without betraying it. The Catechism of the Catholic Church covers this:
2489 Charity and respect for the truth should dictate the response to every request for information or communication. the good and safety of others, respect for privacy, and the common good are sufficient reasons for being silent about what ought not be known or for making use of a discreet language. the duty to avoid scandal often commands strict discretion. No one is bound to reveal the truth to someone who does not have the right to know it.282- CCC
Therefore, when our Lord asks us to be always ready, it seems that one of the things to be ready for is to know how to use discreet language is grave situation to protect the sanctity of truth. Often we are caught by surprise and lie in the confusion of the moment, and later we comfort ourselves that God will understand, after all we had a good intention. But sin is still sin. Peter cut off the roman soldiers ear in a moment of confusion and protective instinct. Jesus did not approve of this. God is still perfect and our weakness can not make him lower his great standard which is really his identity: God does not change; Truth is who He is.
In great suffering, the great role model can be none other than the Blessed Mother.
Mary suffered for Jesus from the beginning to end. She risked a break up with Joseph, she became a refugee in Egypt, and more... all the way through the Passion and the Cross. She is never reported trying to spare him or his friends from suffering. On the contrary, she seems to be a great sign of comfort and hope in the love of God which never abandon us.
In conclusion, suffering is terrible. Jesus told us that we must pick up our cross and follow him if we expect to be with him in Paradise. But he did not tell us to be stupid and expose ourselves to situation of temptations. On the contrary, he taught us to pray so that we are spared from temptations. Perhaps he wants us to be spared from terrible suffering. It is not easy to resist temptations in the face of great suffering and death. He suffered greatly in Gethsemane "…and his sweat became as drops of blood running down upon the ground." But "he prayed and an angel came to comfort him."(Luke 22) When we say that lying is okay sometimes, we are basically saying that Jesus never went pass Gethsemane. There he was terrified to death, and as usual the devil proposed a way out. The Lord Jesus showed us the terror on the flesh, and its desire that the cup of suffering be taken away, but by his prayer, he reminded us of the priority of the spiritual life over physical life. The spirit is willing but the flesh is weak, so he ask his Father, "not my will, but your will be done". Muslims believe, God took him up, and deceived people by showing an other person and getting them to believe that it is was Jesus they were torturing and crucifying. This explains why they believe that lying is okay sometimes, after all, God lied himself to save Jesus. However, we Christians believe that God is almighty, not only God is truth itself, but why would the all powerful one feel a need to lie? isn't truth powerful enough to defend itself? This is the Christian Faith, truth is all powerful and can conquer everything including death. And this is what Jesus went on to prove, because he is the truth incarnate. He went beyond Gethsemane to the cross and beyond, he conquered suffering and death, and went back to the Father to send us his power: the Holy Spirit. The Holy Spirit is the Spirit of Truth, the power of true love. It empowers us to witness to the truth in all things. To prove that real life is in the truth not in the flesh. The Holy Spirit reveals to us that those who die in the truth are alive while those who are in the flesh but lives in falsehood are dead.
Eternal life is life in the truth. Lying for Jesus is like cutting the branch one is seating on. The effects may not show immediately but they will eventually show. Let's pray the Holy Spirit never to leave us but to empower us never to shy away from our crosses, but to pick them up and carry them to the end.